Atrial fibrillation is a common cardiac arrhythmia involving the atria of the heart. During atrial fibrillation, the atria beat irregularly and out of coordination with the ventricles of the heart. Atrial fibrillation disrupts efficient beating of the heart and may result in blood clotting in the atrium leading to serious medical conditions such as strokes.
Atrial fibrillation is generally caused by abnormal electrical activity in the heart. During atrial fibrillation, electrical discharges may be generated by parts of the atria which do not normally generate electrical discharges, such as pulmonary vein ostia in the atrium. Pulmonary vein isolation is a common medical procedure for treatment of atrial fibrillation.
Ablation technologies currently include unipolar and bipolar techniques. The unipolar techniques employ various energy sources, including radiofrequency (RF), microwave, high intensity focused ultrasound (HIFU), laser, and cryogenic energy sources. The bipolar techniques employ RF energy.
U.S. Pat. No. 7,326,201 to Fjield et al. describes a collapsible ultrasonic reflector which incorporates a gas-filled reflector balloon, a liquid-filled structural balloon, and an ultrasonic transducer disposed within the structural balloon. Acoustic energy emitted by the transducer is reflected by a highly reflective interface between the balloons. In a cardiac ablation procedure, the ultrasonic energy is described as being focused into an annular focal region to ablate cardiac tissue extending in an annular path along the wall. Devices for stabilizing the balloon structure and for facilitating collapse and withdrawal of the balloon structure are also described.
U.S. Patent Application Publication 2006/0100514 to Lopath describes a cardiac ablation procedure, in which ultrasonic energy is emitted from an ultrasonic ablation device and is focused on myocardial tissue within the wall of the heart or within the wall of a blood vessel connected to the heart. Ultrasound attenuation of the cardiac tissue is described as being selectively increased by introducing microbubbles into the circulatory system of the subject so that the microbubbles enter the coronary arteries and pass into the myocardial tissue.
The following patents and patent applications may be of interest:    U.S. Pat. No. 5,776,063 to Dittrich et al.    U.S. Pat. No. 6,605,084 to Acker et al.    U.S. Pat. No. 6,635,054 to Fjield et al.    U.S. Pat. No. 7,311,701 to Gifford et al.    U.S. Pat. No. 7,565,191 to Burbank et al.    U.S. Patent Application Publication 2005/0080469 to Larson et al.    U.S. Patent Application Publication 2006/0241523 to Sinelnikov et al.    U.S. Patent Application Publication 2007/0239077 to Azhari et al.    U.S. Patent Application Publication 2008/0058682 to Azhari et al.    U.S. Patent Application Publication 2008/0033415 to Rieker et al.    U.S. Patent Application Publication 2009/0247912 to Warnking    PCT Publication WO 2003/097162 to Vortman et al.
The following references may be of interest:    Buch E et al., “Intra-pericardial balloon retraction of the left atrium: A novel method to prevent esophageal injury during catheter ablation,” Heart Rhythm 2008; 5:1473-1475    Cassak D, “Endosense: Facing technology and financing challenges in AF,” IN-VIVO: The Business & Medicine Report, 36-44, March 2010    Di Biase L et al., “Prevention of phrenic nerve injury during epicardial ablation: Comparison of methods for separating the phrenic nerve from the epicardial surface,” Heart Rhythm 2009; 6:957-961    Matsuo S et al., “Novel technique to prevent left phrenic nerve injury during epicardial catheter ablation,” Circulation 2008; 117:e471    Nakahara S et al., “Intrapericardial balloon placement for prevention of collateral injury during catheter ablation of the left atrium in a porcine model,” Heart Rhythm 2010; 7:81-87    Shen J et al., “The surgical treatment of atrial fibrillation Heart Rhythm,” Vol 6, No 8S, August Supplement 2009.    Sacher F et al., “Phrenic Nerve Injury After Catheter Ablation of Atrial Fibrillation,” Indian Pacing Electrophysiol J. 2007 January-March; 7(1): 1-6.    Schuessler R B et al., “Animal studies of epicardial atrial ablation,” Heart Rhythm, Vol. 6, No 12S, S41-S45, December Supplement 2009